[2.0] Renaming orm:generate-entity-stubs to orm:generate-entities to be consistent and fixed a few bugs

[2.0] Refactoring AnnotationExporter code to a EntityGenerator tool which is used now in orm:convert-mapping to generate annotated entities and also used in orm:generate-entity-stubs for generating entity classes and properties/method stubs from mapping information

[2.0] Extracting Doctrine 1 schema conversion from orm:convert-mapping task to a orm:convert-d1-schema task